1. Field of the Invention
The present invention relates to a lawn mower which includes a cutter and a discharge fan that are rotated by an engine on the lawn mower.
2. Description of the Relevant Art
Some lawn mowers comprise a cutter housing, an engine mounted on the cutter housing, and a cutter blade and a discharge fan which are disposed in an inner space beneath the cutter housing and rotated by the engine. One such lawn mower is disclosed in U.S. Pat. No. 3,696,595, for example. The disclosed lawn mower is propelled by the hands of the user. Grass clippings cut off by the cutting blade in the cutter housing are discharged laterally out of an outlet defined in a housing side wall, by a twisted portion of the cutter blade and air streams caused by the discharge fan.
In the conventional lawn mower, the cutter blade rotates at a higher speed than the discharge fan. During rotation of the cutter blade, its twisting portion produces turbulent airflows. These turbulent airflows impinge on each other and also on the cutter blade, thereby producing wind noise. The generation of the turbulent airflows, which are primarily responsible for the wind noise, is related to the thickness of a turbulent boundary layer which is produced when air flows along the surface of the cutter blade. The thickness of the turbulent boundary layer is proportional to the distance over which the air flows along the cutter blade surface.
The present invention has been made in an effort to eliminate the aforesaid drawback of the conventional lawn mower.